1. Field of the Invention
The present invention relates to ion implantation, and, more especially, to a method of setting up a medium current ribbon beam for ion implantation and an ion beam system.
2. Description of the Prior Art
Ion implantation is a process used to introduce into a target substrate atoms or molecules, generally referred to as dopants, to make materials with useful properties. In the field of processing materials with ion beams, various techniques have been developed for producing large, approximately-parallel ribbon ion beams with controlled current uniformity.
Use of a ribbon beam for high current implantation is well known (U.S. Pat. No. 7,326,941, U.S. Pat. No. 7,462,843, U.S. Pat. No. 5,350,926 and U.S. Pat. No. 5,834,786). Uniform application of ions extracted from an ion source to a target is achieved by making the ion intensity distribution highly uniform at the target in the long dimension, and by translating the target in a direction substantially parallel to the short dimension.
In practice, a common target of ion beams is a silicon wafer. For high current implantation of 300 mm wafers, the total current of ions extracted from the ion source is in the range from about 10 mA to about 100 mA. The total intensity of ions in the part of the ribbon beam which strikes the wafer varies from about 3 mA to about 30 mA. The desired ion dose delivered to the wafer is generally in the range from 1E14 to 5E15 ions/cm2. The energy of ions implanted into the wafer is in the range from 0.2 keV to about 20 keV, with ions being extracted from the ion source at 8 keV to 20 keV and subsequently decelerated as required.